JPH0729350B2 - Injection molding method with pressurization - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an injection molding method involving press-pressurization, and more particularly to an injection molding method involving press-pressurization that is optimal for molding a product such as an optical lens that requires high molding accuracy and compositional homogeneity. More specifically, the cavity formed in the mold is pre-expanded to a volume greater than or equal to a sufficient volume to prevent the inflow of the resin, and is maintained at a temperature at which the resin remains in a fluid state. A thermoplastic resin in a molten state heated in the expanded cavity is pre-measured and injected in an amount more than that required for obtaining a molded article. Cavity shrinks before all of the pre-weighed thermoplastic is injected into the entire cavity. In this cavitating reduction operation, when the cavitating is reduced to a volume obtained by adding the volume of the molded article and the molding shrinkage amount due to the cooling of the thermoplastic resin, there is no unfilled portion that causes a flow mark in the cavity. Is controlled like. When the cavity is reduced, the thermoplastic resin that may have been overcharged to the cavity does not prevent the thermoplastic resin from backflowing from the cavity due to the reduction of the cavity and may remain in the cavity. The injection pressure is reduced to a pressure at which the resin can be injected into the part. When the cavity is reduced to a volume that is the sum of the volume of the molded article and the molding shrinkage amount due to the cooling of the thermoplastic resin, the sprue is sealed, and the thermoplastic resin is cooled to the temperature under pressure and the product is taken out. .

[Prior art and its problems]

The following is a representative example of a conventionally known typical prior art for obtaining a molded article from a thermoplastic resin by injection molding. First, in order to prevent the formation of weld marks on the surface of a molded article, the cavity is expanded in advance, and the thermoplastic resin in a molten state, which is pre-measured to the amount necessary to obtain the molded article, is expanded. Eject into the cavity. After this injection operation is completed and the gate is sealed, the thermoplastic resin injected into the cavity is subjected to mold clamping force, and the thermoplastic resin is cooled to the temperature for obtaining a molded article. However, the above conventional example causes the following problems. First, in the case where one mold device has two or more cavities, it is extremely difficult to make the inflow easiness of resin into each cavity completely equal. Therefore, a larger amount of resin is injected into the cavity into which the resin easily flows, and the amount of resin filled between the cavities tends to be unbalanced. Furthermore, since the cavity is expanded to prevent weld marks, the flow of the resin will stop with a large unfilled portion left inside the cavity when the injection operation of the measured resin is completed, and the filled portion Flow marks are likely to occur on the critical line of the unfilled part. Further, photoelastic strain also occurs at the location where the flow mark is generated. Next, the following is known as another prior art example. First, in order to prevent the formation of weld marks on the surface of the molded article, the cavities are expanded in advance, and the molten thermoplastic resin is completely filled in the expanded cavities. Next, the cavity is reduced and the overfilled thermoplastic resin is backflowed from the cavity without gate sealing. After the cavity is reduced to a desired volume, a gate seal is made, and then the thermoplastic resin is cooled and cured under pressure. However, this conventional example has a problem that photoelastic strain is likely to occur near the entrance of the cavity due to a large amount of backflow. Further, any of the above conventional examples has the following problems. That is, when a thermoplastic resin is cooled and cured from a high-temperature molten state, its dynamic elastic modulus changes and hardens, but the dynamic elastic modulus does not change linearly in the entire temperature range during cooling. It has the property that the dynamic elastic modulus changes rapidly at the temperature (glass transition point Tg). For this reason, if a temperature difference occurs in each part of the resin when passing through the glass transition point during cooling, the resin in the cavity will have a solidified portion and a molten portion. In the conventional molding method, when the glass transition point is passed, the pressurizing step is performed without paying special attention to the temperature deviation generated in each resin portion.
The solidified portion is prone to plastic deformation and the internal composition is likely to be inhomogeneous.

[Object of the Invention]

The present invention aims to solve such problems. More specifically, the present invention is an injection with pressurization that does not cause an imbalance in the amount of filled resin between a plurality of cavities caused by expanding the cavities to prevent weld marks during injection. A molding method is provided. In addition, according to the present invention, at the time when the injection operation is completed, the pressurization which does not cause the flow mark and the photoelastic distortion caused by the stop of the resin flow while leaving the large unfilled portion in the cavity is performed. An associated injection molding method is provided. In addition, the present invention provides an injection molding method involving press pressing, which does not cause photoelastic distortion caused by backflow of a large amount of resin from the cavity when the cavity is reduced. Further, the present invention prevents a state in which a solidified portion and a molten portion are mixed due to a temperature difference inside the resin when the resin being cooled passes through the glass transition point to the low temperature side. Thus, there is provided an injection molding method involving pressurization, which can prevent the internal composition of a molded article from becoming inhomogeneous and from causing compositional deformation of a rapidly solidified portion.

[Outline of the Invention]

The invention described in claim 1 uses a mold having at least one cavity, a so-called gate seal mechanism for opening and closing a spool portion through which molten resin passes, in an injection molding machine having a pressurizing device, and This is a method of molding a lens of high precision. First, the mold temperature is set to a temperature at which the resin flows smoothly under normal pressure, and the volume of the cavity is set to a width large enough for the resin to flow freely. The width at this time is the sum of the volume of the lens at room temperature, the amount of shrinkage from the molten state, and a slight margin. In this state, the measuring device measures the molten resin and starts injection. It should be noted that the amount of measurement is slightly larger than the amount necessary to obtain only the lens. With the above configuration, the flow rates of the resin to the plurality of cavities can be made substantially equal. Next, when the tip of the injected resin passes the optical axis which is the center of the lens, the contraction of the cavity is started. If the injected resin passes the optical axis of the lens, there is nothing that hinders the resin flow, and hence the cavity starts contracting from this point. The target value of the cavity volume at the time of completion of contraction is the sum of the volume of the lens at room temperature and the contraction amount due to cooling. During this reduction operation, the injection pressure is set to a pressure sufficient to fill the unfilled portion with the resin. Immediately before the reduction reaches the above target value, the filling is completed in the pressure-holding state, and the cavity is continuously reduced. By this operation, excess resin is backflowed. The gate of the spool section is closed when the reduction amount reaches the target value. With the above configuration, it is possible to prevent the flow of the resin from being stopped while the unfilled portion remains in the cavity when the injection operation is completed. Finally, the mold is cooled and the holding pressure is lowered. The invention of claim 2 is novel in that the holding pressure is lowered according to the resin temperature while cooling the mold of the invention of claim 1. That is, since the dynamic elastic modulus is increased by cooling, the pressure applied to the resin is reduced along with the increase. That is, this configuration prevents the solid portion and the molten portion of the resin from being mixed.

【Example】

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
It The injection used in the molding method of the present invention is shown in FIGS. 1 and 2.
An example of a compression molding apparatus is shown. The tie bars 2 planted in the four corners of the fixed side die plate 1
Cylinder fixing plate with mold clamping cylinder 3 mounted on the upper end
The seat 4 is fixed. The movable side die is attached to the tip of the piston 5 of the mold clamping cylinder 3.
Rate 6 is stuck. This movable die plate 6
Along the tie bar 2 due to the forward and backward movement of the piston 5.
Up and down. The lower die plate 7 is fixed on the upper surface of the fixed die plate 1.
The lower die insert 8 and the lower die plate 7 are
And 9 are stored. The upper die suspension member 10 is fixed to the lower surface of the movable die plate 6.
Has been done. The upper die 11 which is in surface contact with the lower die plate 7 has bolts 12 and
And 13 are suspended from the upper die suspension member 10,
Of the compression spring 14 and the bolt 13 provided around the bolt 12.
The compression spring 15 provided around the upper and lower suspension members 10 and
Generates repulsive force between rate 11. In the upper mold plate 11, directly above the lower mold inserts 8 and 9.
Upper mold inserts 16 and 17 can be moved up and down to corresponding positions
It is provided in. Head flanges 16a and 1 of upper mold inserts 16 and 17, respectively
7a exists in the internal space 10a of the upper die suspension member 10, and
The head flanges 16a and 17a of the
Is supported in the internal space 10a of the upper suspension member 10,
The upper end surfaces of the head flanges 16a and 17a are movable die plates.
It is in contact with the lower end surface of 6. The compression springs 18 and 19 are fitted on the inner circumference of the compression springs 18 and 19, respectively.
Provided with return pins 20 and 21 respectively for guiding
There is. As shown in more detail in FIG. 2, below each tie bar 2.
An auxiliary cylinder 22 is screwed on the end of the auxiliary cylinder.
The tip of the piston 23 of the da 22 penetrates the lower flange 24.
It is screwed into a bottomed tubular case 25. A pin 26 is erected on the upper end surface of the case 25.
26 passes through the through hole formed in the fixed side die plate 1.
It is in a state where it can be raised and lowered. A vertically long spacer ring 27 is arranged around the tie bar 2.
The lower end surface of the spacer ring 27 is
It is supported. Next, an injection system for measuring and injecting the molten resin
A plunger 29 is provided in the Linda 28
The jar 29 is driven by a drive mechanism such as a hydraulic cylinder (not shown).
The cylinder 28 is moved forward and backward. The nozzle 28a of the injection cylinder 28 is the sprue 3 of the lower mold plate 7.
It is connected to 0 and the sprue 30 is the lower mold plate 7 and the upper mold.
Via the runner 31 formed on the joint surface with the plate 11
Connected to gates 32a and 33a of cavities 32 and 33, respectively.
Has been. The stator 34a fixed to the fixed die plate 1 and
The mover 34b fixed to the movable die plate 6
Is the position where the position of the movable die plate 11 is detected by both
It constitutes the sensor 34. More specifically, the stator 34a and the mover 34b are, for example, potentiometers.
Composing a scooter and moving the movable die plate 6 up and down.
Therefore, the relative position of the mover 34b with respect to the stator 34a changes.
It And the stator 34a is fixed in position
The output of the position sensor 34 is primarily the movable die
The position of the door 6 is shown. As the movable die plate 6 moves up and down, the upper die in
Sarts 16 and 17 move up and down, and upper mold inserts 16 and
The volumes of cavities 32 and 33 are determined according to the lifting position of 17
Since the output of the position sensor 34 is
B. It shows the volume of 32 and 33. 35 is a position sensor for detecting the position of the plunger 29.
is there. The position sensor 35 is directly connected to the plunger 29.
The plan at the end of the preliminary weighing operation.
Injecting operation when position P of jar 29 is fixed
The difference between the current position of the plunger and the initial position P is the injection
It corresponds to the amount of resin applied. Therefore, the output of the position sensor 35
The amount of injected resin can be known. Next, referring to the above matters, the acrylic resin is prepared by the method of the present invention.
Explain the operation when forming a minus lens from oil
U The flow chart shown in FIG. 3 is for understanding the present invention.
It will be easy. First, the raw material acrylic resin is heated to a molten state.
is there. Furthermore, the temperature inside the cavities 32 and 33 is usually acrylic resin.
Adjusted to 130 ℃, which is the temperature that can maintain the fluid state under pressure.
Has been. In addition, the hydraulic circuit connected to the port 22a of the auxiliary cylinder 22
The path is unobstructed and its piston 23 is
It is ready to go up and down. In other words, the auxiliary cylinder 22
The movable die plate 6 is in a state where it does not hinder the lowering of the die plate 6. After this initial setting operation, oil is added to the port 3a of the mold clamping cylinder 3.
Is supplied, the piston 5 advances and the movable die plate
Lower 6 The upper die suspension member 10 is also lowered by lowering the movable die plate 6.
Then, the upper die plate 11 also descends via the bolts 13. So
Then, it occurs between the upper die suspension member 10 and the upper die plate 11.
The upper mold put 11 and the lower mold play by the separating force of the compression spring 15.
And 7 are joined. In addition, when the movable die plate 6 is lowered, the movable die is
The lower surface of the flat plate 6 and the upper flaps of the upper mold inserts 16 and 17
Since the lunges 16a and 16b are in contact, the upper mold insert
16 and 17 also descend. As the upper mold inserts 16 and 17 descend, the cavities
The volumes of 32 and 33 are decreasing, and eventually the cavities of 32 and 33 are reached.
The volume of 33 and 33 is the value of the lens to be molded at room temperature and normal pressure.
It is reduced to a volume equivalent to 150% of the volume. In addition, this 1
The value of 50% is the act that flows into cavities 32 and 33.
The volume required to prevent split flow of the rill resin.
It depends on the shape of the cavity and the fluidity of the resin.
The volume of the cavities 32 and 33 at this time is the target lens.
Accumulate more acrylic resin than required to mold
Volume is required. Cavity that fluctuates as the movable die plate 6 descends
The volumes of 32 and 33 are detected by the position sensor 34. Ki
The volumes of cavities 32 and 33 are
Reduced to a volume equivalent to 150% of the volume at room temperature and pressure
When the output of the position sensor 34 indicates that
Activates and fixes the volumes of cavities 32 and 33 at that position
To do. More specifically, it is connected to the port 22a of the auxiliary cylinder 22.
The hydraulic circuit is blocked by a shutoff valve, etc.
As a result, the position of the piston 23 is fixed. This piss
The upper end of the cap 25 connected to the tongue 23
Since the pacer ring 27 is installed, the position of the piston 23
The spacer ring 27 can be lowered by
Regulated. As a result, the spacer ring 27 covers the movable die plate 6.
Since it is supported at the position, the volumes of cavities 32 and 33 are fixed.
To be done. At the same time, the propulsive force of the mold clamping cylinder 3 also becomes
It is controlled to fix the volume of the tees 32 and 33. In this way the volumes of cavities 32 and 33 are
A volume equivalent to 150% of the volume of the lens to be used at room temperature and pressure
Pre-weighing operation by injection cylinder 28 when fixed by product
Is executed. First, in the injection cylinder 28, a screw mechanism (not shown) and others
When the molten resin is injected from the mechanism of
Is retracted in the injection cylinder 28 by the resin pressure. Plunge
The amount of retreat of the chamber 29 is equal to the amount of resin flowing into the injection cylinder 28.
Correspondingly, the amount of retraction of this plunger is determined by the position sensor 35.
Detected. Then, when the plunger 29 retracts to the position P, the injection is performed.
The cylinder 28 has more actuators than necessary to get the lens.
Lil resin accumulates. The position sensor 35 indicates that the plunger 29 has retracted to the position P.
The pre-weighing operation is completed by the output of
Transition to injection operation. The resin injection operation is performed by raising the plunger 29.
Is done. The plunger 29 is injected with a hydraulic cylinder (not shown).
When it rises in the binder 28, it is ejected by the above preliminary weighing operation.
The acrylic resin accumulated in the cylinder 28 is stored in the nozzle 28a.
-Through the sprue 30-runner 31-gates 32a and 33a,
It flows into the cavities 32 and 33. At this time, the temperature inside the cavities 32 and 33 is the material
The temperature is set to 130 ° C, which is the temperature at which
The acrylic that has flowed into cavities 32 and 33.
The resin remains fluid. In addition, the volumes of cavities 32 and 33 at this point are
150% of the volume of the article to be molded at room temperature and pressure
Since it has been expanded to the equivalent volume, the injected resin
Flows into the cavities 32 and 33 without diversion,
There is no weld mark. At this time, the left and right
The amount of resin flowing into the pits 32 and 33 is not always uniform.
There is no guarantee, fluid resistance is relatively small and it is easy to flow in
More inflow to one of the cavities. The output of the position sensor 35 also changes as the injection operation progresses,
Know the amount of resin injected by the output of the position sensor 35
be able to. By the way, it is necessary to reserve more than the amount necessary to obtain molded articles.
Cavities 32 and 33 after injection of the total amount of resin weighed
If the volume of the
Backflow of a large amount of resin from cavities 32 and 33
Light near the gates 32a and 33a of the cavities 32 and 33.
Elastic strain occurs. Therefore, in the present invention, a large amount of backflow occurs during mold clamping.
In order to prevent the
Cavity 32 by lowering the upper mold inserts 16 and 17 forward
Cavities 32 and 33 are significantly reduced by reducing the volume of
Do not overfill. On the other hand, at the initial stage of injection operation, the cavities 32 and 33
When the volume is reduced, the resin inside cavities 32 and 33
A divergence occurs in the flow, and a weld line starts at the confluence.
To live. Therefore, in the present invention, the volumes of the cavities 32 and 33 are reduced.
Cavity to the extent that weld lines do not occur
Cavitation is performed when the resin flows into 32 and 33.
B. The operation of reducing the volume of 32 and 33 is started. Proper timing to reduce the volume of cavities 32 and 33
Depending on the nature of the resin and the shape of cavities 32 and 33.
different. For example, when forming a minus lens from acrylic resin
Then the tip of the resin flowing into cavities 32 and 33
After passing through the position of the optical axis of the lens (ie, flowing
The tip of the resin ensures the narrowest part of the thickness of cavities 32 and 33.
(After passing to the)
Is desirable. In addition, the start of reduction of the cavity volume
For each cavities 32 and 33 when making iming decisions
The difference in ease of resin inflow must be considered. 4 to 7, the right side cavity 32 is on the left side.
Fluid resistance is relatively smaller than that of cavities, and resin flows
It is created on the assumption that it is easy to enter. or,
The% figures shown in these drawings are
Of the cavities 32 and 33 based on the volume of the lens
Shows the product. First, Fig. 4 shows the case where the resin is difficult to flow in due to the large fluid resistance.
Of the resin 36 that has flowed into the cavity 33 of the
It shows the state of passing through the storage. An amount of resin equivalent to 90% of the pre-measured resin was injected.
Inside the cavities 32 and 33 when the injection operation progresses until
It is an attempt to change the state of to the state shown in Fig. 4.
90% of the pre-measured resin
The injection operation has progressed until the appropriate amount of resin has been injected.
After the output of the position sensor 35 indicates and
Shift to the reduction operation of. However, the reduction of this cavity volume
The injection operation of the resin 36 continues during the small operation. When reducing the cavity volume, first of all, the auxiliary cylinder 22
The shield of the hydraulic circuit of the port 22a is released. The hydraulic circuit connected to port 22a is unshielded.
Spacer ring 27, pin 26, case 25, piston 23
It does not hinder the lowering of the moving die plate 6. In addition, the following
No reference to auxiliary cylinder 22 in the description
However, when the mold clamping cylinder 3 moves forward, the hydraulic pressure of the auxiliary cylinder 22
The circuit is unshielded and the cavity position is fixed.
The hydraulic circuit of the auxiliary cylinder 22 is closed at a fixed time. Then, oil is supplied to the port 3a of the mold clamping cylinder 3 and the upper mold a
By lowering inserts 16 and 17,
The volumes of 32 and 33 are reduced. At this time, the injection pressure of the resin by the plunger 29 is 100 kgf.
/cm ² To lower. In addition, this 100kgf / cm ² Injection pressure
The meaning of power will be described in detail later. Continuous supply of resin from injection cylinder 28 and cavitation
B. Inside the cavities 32 and 33 due to the volume reduction of 32 and 33
The resin 36 that has flowed into
Go on. 100kgf / cm with this plunger 29 ² Resin at injection pressure of
The injection operation of cavities 32 and 33 by the mold clamping cylinder 3
Was performed in parallel with the volume reduction operation of
Volume of cavities 32 and 33 when 95% of the resin is injected
Is reduced to 110% of the molded lens volume
Controlled. The value of 110% is also used for the properties of resin and cavitation.
A numerical value that fluctuates depending on the shape of a
Absent. Therefore, the meaning of this value of 110% and the above 100
kgf / cm ² The meaning of the injection pressure will be described in more detail. The molded lens volume is 100%, and the left and right cavities are
B Holding pressure to stabilize the amount of resin flowing in 32 and 33
30kgf / cm ² And cooling from the state where this holding pressure is applied
If the molding shrinkage rate due to
Is completed and the sprue is sealed by the sprue cutter 37.
When the cavities 32 and 33 have a
Needs to be 105% of the volume. Then, for example, as shown in FIG.
Cavity 32 is completely filled when 95% is ejected
Assuming that the Cavity 32 is 110% and 105%
5% equivalent volume and 100kgf / cm ² Injection pressure of 30
kgf / cm ² Difference of holding pressure of 70kgf / cm ² Equivalent to pressure
The amount is overfilled. Therefore, the volume of the cavity 32 is made equal to the volume of the molded lens.
Equivalent to 105% of volume
When the volume is reduced to
It will be backflowing from Vity 32. And this
The amount of backflow that occurs at
Photoelastic strain is generated near the gate 32a of the cavity 32.
It Therefore, the above-mentioned numerical value regarding the volume of 110% and the above
100kgf / cm ² The numerical value related to the pressure is
32 volumes correspond to 105% of the volume of the molded lens
The injection pressure is the holding pressure as well as the volume is reduced.
30kgf / cm ² Of backflow that occurs when
The amount is determined so that the amount does not exceed the allowable value. Similarly, 95% of the above pre-weighed resin was injected
At the time of molding the cavities 32 and 33 volumes of the lens
With this 95%, it will be reduced to a volume equivalent to 110%.
The numerical value also depends on the properties of the resin used and the shape of the cavity.
Therefore, it is a fluctuating number and not a fixed number. So I will explain the meaning of this 95% in more detail.
It Due to the difference in ease of resin flow to cavities 32 and 33
Due to this, the volumes of cavities 32 and 33 are molded
Fig. 5 at the time when the volume is reduced to 110%
Even if Cavity 32 has completely filled, as shown
The cavity 33 may have an unfilled portion remaining. At this time, the cavity 32 is completely filled, so
A large internal pressure is generated in the duty 32, and the fluid resistance is suddenly increased.
To the cap with the unfilled part remaining.
The fluid resistance of the bite 33 is still low, so
B. Resin injected after 32 is completely filled
Most of the flow into Cavity 33. In addition, the volumes of cavities 32 and 33 are adjusted to reduce molding shrinkage.
105% of the molded lens with the expected volume
In the process of shrinking with a volume equivalent to
Injection from the resin or injection cylinder 28
The resin flows into the cavity 33. And this cavity
Inflow of resin to 33 and reduction of capacity of Cavity 33 itself
As a result, the unfilled part remaining in the cavity 33 is resin.
Will be filled with. However, the lens in which the capacity of the cavity 33 is molded
The volume is reduced to 110% of the volume of
Larger than some unfilled portion remaining in cavity 33
If not, the capacity of the cavity 33 is
Even when the volume is reduced to 105% of the volume,
The unfilled portion remains in the cavity 33. Therefore, the difference in the ease of resin inflow of cavities 32 and 33
If the maximum value is taken into consideration, the cavities that are more likely to flow resin
The tee 32 is not overfilled, which causes photoelastic distortion.
The volume of the lens that does not and has a large cavity volume
Resin flow when the volume is reduced to 105% of the product volume
The unfilled part remains above the cavity 33 that is difficult to enter.
The above value of 95% is decided so that it will be in the range that does not exist
To be done. Now, the resin equivalent to 95% of the pre-measured resin is injected.
When the position sensor 35 detects that the
・ 33 volumes correspond to 110% of the volume of the molded lens
The mold clamping cylinder 3 is controlled so that the volume becomes
Injection pressure of resin by Ja 28 is 30kgf / cm ² Down to
It Therefore, this 30kgf / cm ² The injection pressure of
The injection operation continues further. The injected resin amount exceeds 95% of the pre-measured resin amount.
However, when the amount of pre-measured resin reaches 96%, the mold clamping series
The amount of oil supplied to port 3a of
10 of the volume of the lens molded volume of 32 and 33
Reduce to a volume equivalent to 5%. The volumes of cavities 32 and 33 are molded as shown in FIG.
Is reduced to a volume equivalent to 105% of the lens volume.
Trees that were overfilled from Cavity 32 in the process
The oil backflows. At the same time, its volume accounts for 110% of the molded lens volume.
It remained in the cavity 33 when the volume was appropriate.
The unfilled part is the capacity of the cavity 33 reduced and
Resin that flows in due to the backflow pressure from the tee 32 and
Injection cylinder 28 to 30 kgf / cm ² Inflow by injection pressure of
Volume of cavities 32 and 33 filled with resin
Is reached when it reaches 105% of the molded lens volume.
The cavity 33 is completely filled. The above 30kgf / cm ² The injection pressure of is the holding pressure described above.
Yes, this holding pressure is due to the cavity that was overfilled.
The back flow from 32 is not hindered and the unfilled part remains.
Can promote resin inflow to existing Cavity 33
It is pressure, and it depends on the shape of the cavities 32 and 33 and the properties of the resin.
Therefore it is different. Now, the volumes of cavities 32 and 33 are formed in this way.
Is reduced to a volume equivalent to 105% of the lens volume
At this point, cavities 32 and 33 are completely filled with resin.
It is filled with cavities 32 and 33 due to the resin filling.
30kgf / cm inside ² Larger pressure than the injection pressure of
There is a possibility that This state is maintained for a certain period of time (
It is usually several seconds although it depends on the shape of the cavity. )
The internal pressures of cavities 32 and 33 reach equilibrium when
To do. After the time required for this internal pressure to equilibrate has elapsed
(Or directly detecting the internal pressure of cavities 32 and 33
And the detected values are both 30kgf / cm ² Balanced with the holding pressure of
The sprue cutter 37 into the sprue 30 as shown in FIG.
And the resin injection operation is completed. After the completion of this injection operation, the pressurizing process is started. First, during the entire process of the above injection operation, the cavity 32
The temperature inside 33 and 33 is the temperature at which the resin can maintain the fluid state.
It is set to 130 degrees. Therefore, the injected resin is heat-exchanged with the mold equipment.
It is cooled down to 130 degrees which is the temperature of the mold equipment.
At this point, the resin inside cavities 32 and 33 remains fluid.
The pressure is evenly applied. Therefore, supply oil to the port 3a of the mold clamping cylinder 3 and
1013kgf / cm for resin inside the bites 32 and 33 ² Pressure
When pressure is applied, this pressure is applied to the resin inside cavities 32 and 33.
Add evenly to. As mentioned above, the thermoplastic resin has a dynamic elasticity as it cools.
It has the property of increasing the rate and hardening, and pressurizing it.
It also has the property of increasing the dynamic elastic modulus and hardening.
Have And the above 1013kgf / cm ² That pressure is a material
Even if the temperature of the kuriru resin is as high as 130 degrees,
Dynamic elastic modulus at normal temperature and temperature (of course acrylic resin glass
To obtain a dynamic elastic modulus that exceeds the dynamic elastic modulus of the dislocation point)
Is the pressure at which the resin can be
Determined by temperature. In this way, the temperature at which the fluid state is completely maintained under normal pressure
Dynamic elasticity of resin at room temperature and pressure
To obtain a dynamic elastic modulus equal to the elastic modulus
The resin in the curing process passes through the glass transition point,
The homogeneity of the internal composition because there is no temperature difference when
It is possible to obtain excellent molded products. The resin thus cured by pressure is then applied to the mold.
It is cooled inside, but with this cooling, the mold clamping cylinder 3a
By controlling the pressure at normal temperature and pressure of the resin
Taking out the resin while maintaining the dynamic elastic modulus at
Cool to a temperature of 95 ° C. The pressure control at this time is performed as follows. First, the resin has the same dynamic elastic modulus as that at normal temperature and pressure.
The pressure required to obtain
It is determined positively, and the lower the resin temperature, the more
Pressure that can maintain a dynamic elastic modulus equal to the dynamic elastic modulus also decreases
It Therefore, in this embodiment, as the resin temperature decreases,
To obtain the dynamic elastic modulus at room temperature and normal pressure at the resin temperature.
Pressure applied to resin from mold clamping cylinder 3a
Lower. In other words, in this embodiment, the resin is cooled.
Clamping cylinder 3a so as to offset the accompanying increase in dynamic elastic modulus
Reduce the pressure applied to the resin. Then, the resin is cooled to the take-out temperature of 95 ° C.
Then, to supply oil to the port 3b of the mold clamping cylinder 3.
Therefore, the movable die plate 6 is raised and the lower die plate
7 Open the joint surface between plate 7 and plate 10 and take out the lens.
You By the method of the present invention described above, the average mass is 18.430 g.
A minus lens with a diameter of 70 mm is molded from acrylic resin
If a similar lens is molded by the conventional molding method,
The following results were obtained when the results were compared. (1). Provided two cavities in a single mold device
In the case of the amount of resin filled between the left and right cavities
difference. The conventional molding method produced an average difference of 4.9%.
The Ming method produced an average difference of 0.5%. (2). Photoelastic strain. When comparing the birefringence that appears as a result of photoelastic strain,
A birefringence of 200 nm / cm was confirmed by the conventional method, and
The method confirmed a birefringence of 20 nm / cm. (3). Occurrence rate of flow marks. The rate of occurrence of flow marks for all molded products is
The value was 3.0% in the method, but 1.0% in the molding method of the present invention.
Became. Based on these numerical values, the molding method of the present invention uses the aspherical optical lens.
For molding products that are difficult to precisely and stably mold
It was confirmed that it can be sufficiently adapted. It should be noted that the present invention does not increase the volume of the molded article due to the cooling of the resin.
It is more than the volume that the shape shrinkage is added and the resin shunt
It has been expanded to a volume greater than that which can be prevented and the resin is allowed to flow.
The cavities set above the temperature to keep them moving
Wafer generated by flow resistance by injecting oil
To prevent the lump mark, the total amount of pre-measured resin
To reduce the cavity volume before the
Therefore, it prevents imbalance of resin inflow between cavities
The injection pressure and the injection volume in the process of reducing the cavity volume.
And the cavity volume by controlling
To prevent the flow of resin from stopping in the
To prevent the occurrence of cracks, and to keep the fluid after injection
The resin in
Raises by curing until a dynamic modulus is obtained
Of the internal composition
It is essential to homogenize and prevent plastic deformation.
Yes, various numerical conditions depend on the type of resin and product shape.
Needless to say, it has to be decided as appropriate. Also, in the above, a minus lens is formed from acrylic resin.
Examples have been described with respect to the case where
The present invention is also applicable to the case where a molded product other than a lens is obtained.
It goes without saying that the law can be applied. As described above, in the present invention, at least from the start of injection,
Even if the tip of the resin that flows into the cavity is
Trees that flow in until they pass through the narrowest part
The cavity volume is expanded to a volume that can prevent the diversion of oil.
And during the period from the start of injection to the end of injection.
At a temperature above the temperature at which the resin can maintain its fluid state
Since the temperature is set, the occurrence of weld marks is prevented.
You can stop. In addition, the present invention can prevent the occurrence of weld marks.
Resin injection progresses up to and total amount of pre-measured resin
Cavity volume reduction operation started before injection
However, with respect to the target volume, that is, the volume of the product,
Cavity is reduced to the volume that allows for the amount of molding shrinkage
In the meantime, the unfilled part does not remain in the cavity and the excess
To control injection pressure and injection volume so that filling does not occur
Prevents imbalance in the amount of injected resin between multiple cavities
be able to. In addition, in the present invention, the resin being injected is kept in a fluid state.
And until the time when the desired amount of resin was injected
Since the resin flow does not stop, it is caused by the resin flow stop.
It is possible to prevent the occurrence of photoelastic distortion and flow marks
It Further, according to the present invention, when the injection operation is completed, the resin
Is at a temperature that keeps it in a fluid state, pressurizing this resin
The resin cures from a fluid state to a solid state as it is cured by
When passing through the glass transition point in the process of transition and hardening of
The temperature difference does not occur, and the internal plasticity becomes non-uniform.
Does not live In addition, in the subsequent cooling process, the motion associated with cooling
By reducing the pressure to offset the increase in the elastic modulus,
The dynamic elastic modulus of the resin during cooling is measured at room temperature and pressure.
Since it maintains the dynamic elastic modulus of
Life can be prevented. Therefore, plastic deformation and inhomogeneity in the resin
It is also possible to prevent the occurrence of photoelastic strain caused by the phenomenon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an injection molding apparatus used in the present invention, which involves direct pressure pressurization, taken along the center line of a mold clamping cylinder, and FIG. FIG. 3 is a cross-sectional view of the injection molding apparatus with pressurization shown in the figure taken along the center line of the tie bar, FIG. 3 is a flowchart showing the operation of the present invention, and FIG. 4 is 90% of the pre-measured resin. Fig. 5 shows the cavities at the time of injection, and Fig. 5 shows 95% of the pre-measured resin.
Figure showing the state of cavities at the time when is ejected,
FIG. 6 is a diagram showing the state of cavities when 96% or more of the pre-measured resin is injected, and FIG. 7 is a diagram showing the states of cavities after gate sealing. 1 ... Fixed side die plate 2 ... Tie bar, 3 ... Mold clamping cylinder 4 ... Cylinder fixing plate 5 ... Piston, 6 ... Movable side die plate 7 ... Lower die plate, 8.9 ... Lower die Insert 10 …… Upper die suspension member, 11 …… Upper die plate 12 ・ 13 …… Bolt, 14 ・ 15 …… Compression spring 16 ・ 17 …… Upper die insert 22 …… Auxiliary cylinder, 27 …… Spacer ring 28 ...... Injection cylinder, 29 ...... Plunger 30 ...... Sprue, 31 …… Runner 32/32 …… Cavity, 32a ・ 33a …… Gate 34 …… Position sensor, 35 …… Position sensor

Claims (2)

[Claims] 1. An injection molding machine which performs an injection molding operation involving pressurizing and a resin molding die which has at least one cavity for molding a lens and which has a gate seal mechanism on a spool portion. In the molding operation, a) the temperature of the portion of the mold that comes into contact with the resin should be higher than the temperature at which the resin flows under normal pressure, and b) the volume of the cavity should be sufficient to allow the resin to flow evenly when flowing into the cavity. Large volume, ie
The cavity volume is a volume that includes the volume of the lens at room temperature and the amount of contraction when the lens is cooled from the molten state to room temperature, and further includes a margin. Weigh a little more than the amount of molten resin and start the injection, d) a portion of the weighed resin has not yet been injected, and
After the resin that has passed through the gate 32a has passed through the optical axis portion of the lens, e) the cavity volume is defined as the volume of the lens at room temperature and the amount of shrinkage until the molded lens is cooled to room temperature. Start shrinking to the added volume, f) When shrinking starts, set the injection pressure to the holding pressure necessary to fill the unfilled part with resin, and g) Just before shrinking reaches the target value, Filling is completed with holding pressure applied, and further shrinking is continued, while shrinking is completed while backflowing the excess resin, h) Sealing the gate of the spool part, and i) Cooling the mold and the resin temperature. According to the above, the holding pressure is lowered and the temperature is lowered to the take-out temperature. 2. The injection molding method with pressurization according to claim 1, wherein a pressure at which a dynamic elastic modulus of the resin at room temperature and normal pressure is obtained with respect to the resin injected into the cavity. In addition, it is cured and the resin cured by pressurization is cooled, and this cooling process is performed until the resin is cooled to the take-out temperature while reducing the applied pressure so as to offset the increase in dynamic elastic modulus accompanying cooling. An injection molding method with pressurization characterized by being continued.